/Engine/Plugins/Animation/IKRig/Source/IKRigEditor/Public/RetargetEditor/IKRetargeterController.h
Call this when IK Rig chain is removed.
void HandleRetargetChainRemoved ( [UIKRigDefinition](API\Plugins\IKRig\Rig\UIKRigDefinition) * IKRig, const [FName](API\Runtime\Core\UObject\FName) & InChainRemoved ) const